Tremor frequency characteristics in Parkinson's disease under resting-state and stress-state conditions

• Peak power and peak frequency of tremor increase simultaneously under stress-state condition.
• Tremor peak frequencies are concentrated around 5 Hz under stress-state condition.
• Low peak frequencies are more likely to increase under stress-state condition.
• The distribution of power spectral density of tremor is symmetrical regardless of conditions.
• Frequency range more activated significantly changes across the conditions.

Tremor characteristics—amplitude and frequency components—are primary quantitative clinical factors for diagnosis and monitoring of tremors. Few studies have investigated how different patient's conditions affect tremor frequency characteristics in Parkinson's disease (PD). Here, we analyzed tremor characteristics under resting-state and stress-state conditions. Tremor was recorded using an accelerometer on the finger, under resting-state and stress-state (calculation task) conditions, during rest tremor and postural tremor. The changes of peak power, peak frequency, mean frequency, and distribution of power spectral density (PSD) of tremor were evaluated across conditions. Patients whose tremors were considered more than “mild” were selected, for both rest (n = 67) and postural (n = 25) tremor. Stress resulted in both greater peak powers and higher peak frequencies for rest tremor (p < 0.001), but not for postural tremor. Notably, peak frequencies were concentrated around 5 Hz under stress-state condition. The distributions of PSD of tremor were symmetrical, regardless of conditions. Tremor is more evident and typical tremor characteristics, namely a lower frequency as amplitude increases, are different in stressful condition. Patient's conditions directly affect neural oscillations related to tremor frequencies. Therefore, tremor characteristics in PD should be systematically standardized across patient's conditions such as attention and stress levels.